Flame retardant diallylic phthalate molding compounds

ABSTRACT

FLAME RETARDANT DIALLYLIC PHTHALATE MOLDING COMPOUNDS WITH SUCH GREATLY IMPROVED THERMAL STABILITY THAT THEY DO NOT RELEASE CORROSIVE GASES DURING EXPOSURE TO TEMPERATURES OF 200*C. AND ABOVE, IN A SEALED ENVIRONMENT, ARE OBTAINED BY THE USE OF HEXABROMOBIPHENYL IN AMOUNTS OF 0.5 TO 20% TOGETHER WITH 5 TO 60% ALUMINA TRIHYDRATE AS SYNERGIST FOR THE HEXABROMOBIPHENYL BASED ON THE ALLYLIC POLYMER. THESE NOVEL COMPOSITIONS CAN CONTAIN REINFORCING FIBERS, FILLERS, POLYMERIZATION INITIATORS, RELEASE AGENTS, COLORANTS, GLASS COUPLING AGENTS, INHIBITORS AND OTHER INCIDENTAL ADDITIVES CONVENTIONALLY USED IN THERMOSETTING MOLDING COMPOUNDS. ALLYLIC MONOMERS ARE NOT REQUIRED IN THE COMPOSITIONS OF THIS INVENTION.

United States Patent US. Cl. 260-4218 6 Claims ABSTRACT OF THEDISCLOSURE Flame retardant diallylic phthalate molding compounds withsuch greatly improved thermal stability that they do not releasecorrosive gases during exposure to temperatures of 200 C. and above, ina sealed environment, are obtained by the use of hexabromobiphenyl inamounts of 0.5 to 20% together with to 60% alumina trihydrate assynergist for the hexabromobiphenyl based on the allylic polymer. Thesenovel compositions can contain reinforcing fibers, fillers,polymerization initiators, release agents, colorants, glass couplingagents, inhibitors and other incidental additives conventionally used inthermosetting molding compounds. Allylic monomers are not required inthe compositions of this invention.

CROSS REFERENCE TO RELATED APPLICATIONS This application is related toUS. Patent Application Ser. No. 95,418, filed Dec. 4, 1970, and is acontinuationin-part of US. Ser. No. 182,853, filed Sept. 22, 1971 andnow abandoned.

This invention relates to diallylic phthalate molding compositions whichare used to produce electrical insulation which is flame-retardant andthermally stable at temperatures of at least 200 C. in a sealedenvironment.

There is a growing need for high temperature resinous materialsparticularly for use as electrical insulation. The trend tominiaturization, for technical reasons, such as shortened circuitlengths, as well as for the more obvious needs for space and weightsavings, are at least in part responsible for the compacting of morecircuits into a given volume which is accompanied by greater heatconcentration, the heat arising from external sources as well asimpedance eiiects within the insulation. It is, therefore,

desirable to have electrical insulation which not only exhibits lowimpedance heating effects, which alone can be functions of temperature,but which is also resistant to heat regardless of source.

Besides heat resistance, electrical insulation should also exhibitresistance to burning because of the constant hazard arising frompotential igniting energy. It appears that at least to some degree theneeds for heat and flame resistance in electrical insulation aremutually contradictory.

The best electrical properties in molded insulation are obtained withnon-polar materials. Absence of strong permanent dipoles andpolariza-ble moieties makes for minimum ionic conductivity anddielectric loss. Flame retardant insulation systems, on the other hand,invariably contain polar groups, and they release free acids or bases atflame temperature. Few materials are sufiiciently nonpolar forelectrical insulation and are yet capable of releasing suflicient acidor base to snufl out flames.

The most common allylic flame retardant electrical insulators are thosecontaining halogenated materials, either as part of the resin system oras additives. Halogens alone require such a high concentration ofpolarity to provide flame resistance that electrical properties suffer.Hence,

3|8 Z 6 ,7 7 7 Patented July 30, 1 974 synergists are normally employedto increase the efiiciency of halogen, apparently by promoting releaseof the halogen acid at flame temperature. The most effective synergistis antimony oxide.

Diallyl phthalate and diallyl isophthalate resins are recognized as goodelectrical insulators at elevated temperatures, the former maintainingexcellent electrical properties (high insulation resistance and lowdielectric loss) at temperatures up to C., while the isophthalate showslittle change at 250 C. Commercial molding compounds based on diallylisophthalate show retention of properties for long periods of time attemperatures well in excess of 200 C. By Arrhenius projection, 50% oforiginal flexural strength is maintained after aging at 215 C. for 20years.

There has been a long search to find flame retardant additives forallylic resins which will not detract from electrical and mechanicalproperties of the resins, particularly at elevated temperatures. One ofthe best of these additives to date has been diallyl chlorendatesynergized with antimony oxide. A similar system based on chlorendicacid-containing polyesters is lower cost but poorer electrically. Thelatter is used commonly in many commercial flame-retarded moldingcompounds. Neither of these additives yield flame-retardant moldingcompounds which exhibit the high level of heat resistance found withallylic resins alone.

A special system in which diallyl chlorendate is precured on antimonyoxide and then added to allylic molding compounds has been developed.However, even this system shows some thermal instability relative to theunmodified resin, although stability is greatly improved overflame-retardant allylic compounds based on diallyl chlorendate monomer.

The thermal stability deficiencies of known flame-retardant allylicresin systems are accentuated when heated in a sealed enclosure whereevolved gases from decomposition are retained. It appears that among theearly decomposition products is hydrogen chloride which has anautocatalytic effect, thereby accelerating the rate of still furtherdecomposition of diallylic phthalate resins. In addition the releasedhydrogen chloride severely attacks metal conductors and other materialsin the environment. It appears that chlorendic acid, whose derivativesuntil now have been considered the best source of halogen, has ameasurable rate of dehydrohalogenation at elevated temperatures, and,once this acid begins to release in an enclosed atmosphere, catastrophicfailure occurs soon after.

In accordance with the present invention, there is provided an additivesystem which can be used as a flame retardant for 'both diallylphthalate and diallyl isophthalate polymers and with no sacrifice inelectrical, mechanical or thermal stability properties of electricalinsulation molded from these diallylic phthalate polymers. This additivesystem consists of (l) hexabromobiphenyl synergized by (2) aluminatrihydrate or alumina trihydrate plus a low level of antimony oxide.This additive system appears unique in the following respects, alldesirable:

(1) It is very effective at low levels, that is, requires half, or less,as much additive for comparable flame resistance.

(2) Surprisingly, hexabromobiphenyl is synergized by low cost aluminatrihydrate which is superior electrically to antimony oxide.

(3) This system does not release hydrogen halide at temperatures up toat least 220 C. in a sealed environment. Hence, there is no corrosion ofmetal inserts or acid attack on other components in the system.

The additive system of this invention is used to render diallylphthalate and diallyl isophthalate molding compounds flame resistant byadditions of 0.5 to 20 percent hexabromobiphenyl and 3 to 60 percentalumina trihydrate, and, perferably, 1.5 to hexabromobiphenyl and 8 to55% alumina trihydrate by weight based on the allylic polymer. Thepercentage of resin in the total composition should be at least 30% byweight of the molding compound.

These novel molding compounds contain a polymerization initiator and cancontain release agents, colorants, glass coupling agents, additionalfillers and other incidental additives in amounts commonly used inthermosetting molding compounds.

Quite surprisingly, the compositions of this invention do not requireadded monomer, which has conventionally been required in diallylicphthalate molding compounds made flame retardant by use of halogenatedaromatic additives.

Diallylic phthalate prepolymers useful in practicing this inventioninclude prepolymers made from the diallylic esters of ortho-, iso-, andterephthalic acids. These diallylic phthalates may be manufactured bypolymerizing a monomeric material to produce a solution of solubleprepolymer in monomer. Polymerization is carried to a point short ofgelation. The prepolymer must then be separated from the unpolymerizedmonomer. This may be done by treatment with a solvent which dissolvesthe monomer and precipitates the prepolymer. Such a general process isdescribed by Heiberger in U.S. Pat. 3,096,310. A conventional method ofseparating allylic prepolymer from monomer, by precipitating theprepolymer in an unreactive liquid precipitant, that is, a solvent forthe monomer and a non-solvent for the prepolymer in a shearing zone, isdescribed by Willard in U.S. Pat. 3,030,341. Prepolymers may also beseparated from unpolymerized monomer by distillation, as disclosed byMednick et al. in U.S. Pat. 3,285,836, issued May 28, 1968. The diallylphthalate prepolymers are solids containing little or no monomer; theycan be stored indefinitely in this form, since they require catalystsand either heat, actinic light or nuclear particle radiation to convertthem to the insoluble or thermoset stage.

A wide variety of water-insoluble, inert fillers may be used inpreparing the molding compounds of this invention. Useful fillersinclude calcium carbonate, both precipitated and wet ground types,calcium silicate (wollastonite), silica, hydrated clays, calcined clays,chalk, calcium sulfate (anhydrous), barium sulfate, asbestos, glass(powered), quartz, aluminum trihydrate, aluminum oxide, antimony oxide,magnesium oxide, inert iron oxides and groundstone such as granite,basalt, marble, limestone, sandstone, phosphate rock, travertine, onyxand bauxite. Additionally, inert fibrous materials, such as syntheticfibers, glass fibers, asbestos and cellulosic fibers, may be used. Up to200 parts by weight of filler and/ or fiber per 100 parts by weight ofpolyunsaturated polymerizable materials-polychlorinated aromaticcompound may be used in these molding compositions.

Fillers, both particulate and fibrous, best used in molding compoundsdesigned for sensitive electrical and electronic applications, should beinert and have a low level of ionic impurities as measured in the WaterExtract Conductance Test described in the examples. Typical usefulfillers include silica, ground glass, clays, preferably calcined clays(aluminum silicate), magnesium silicate, wollastonite (calciumsilicate), quartz, alumina, alumina trihydrate, and antimony oxide.Inert fibrous fillers useful in practicing this invention include, butare not limited to, glass fibers, synthetic polymeric fibers such aspolyester fibers, acrylic fibers, and nylon fibers and mineral fiberssuch as asbestos fibers.

Catalysts known to be useful for accelerating the cure of diallylicphthalate molding compositions are generally useful in practicing thisinvention. These catalysts include t-butyl perbenzoate, dicumylperoxide, 2,5-dimethylhexane2,5-diperbenzoate and other catalysts thatcure diallylic phthalate prepolymers at elevated temperatures.

Additional additives found useful in practicing this invention and whichare commonly used in diallylic molding compounds are glass couplingagents, internal mold release agents, selected pigments and inhibitors.Useful glass coupling agents include vinyl-tris (Z-methoxyethox'y)silane and gamma methacryloxypropyl-trimethoxysilane. Internal moldrelease agents useful in diallylic phthalate molding compositions arealso useful in practicing this invention, and these include fatty acidssuch as lauric acid and salts of fatty acids such as calcium stearate.In some cases it is desirable to include in these novel moldingcompounds an inhibitor such as hydroquinone or other inhibitors known tobe useful in diallylic phthalate molding compositions to retard cure.

The novel molding compositions of this invention are prepared inconventional equipment and using techniques well known in the plasticsindustry to be useful in compounding allylic, epoxy, and polyestermolding compounds. The molding compounds may be filled or unfilled andof the premixed, powdered, granular or dough type.

The following examples are provided to illustrate this inventionfurther. The proportions in the examples are by weight unless otherwiseindicated.

The test methods appearing in the following list were followed intesting the molded test specimen made from the various compositionsdisclosed in the examples.

(A) Flexural strength ASTM D-790.

(B) Modulus of elasticity in flexure (flex.

mod.) ASTM D-790. (C) Arc resistance ASTM D-495. (D) Izod impact ASTMD-256. (E) Insulation resistance ASTM D-257. (F) Deflection temperatureASTM D-648. (G) Water absorption ASTM D-570. (H) Specific gravity ASTMD-792. (I) Dielectric constant (D.C.) ASTM D-l50. (J) Dissipation factor(D.F.) ASTM D-150. (K) Volume and surface resistivity ASTM D-257.

(L) Flame resistance, helical coil, ignition and burning time ASTMD-229. (M) Hardness (Rockwell M) ASTM D-785. (N Water ExtractConductance Test Federal Standard LP 406.

The wet test is conducted on samples which were conditioned by immersingthe samples for 24 hours at 23 C. in distilled water, removing thesamples, blotting them dry and then testing the samples as soon aspractical according to the test method.

The diallyl phthalate prepolymers used in the following formulationswere dissolved in suflicient acetone to make a solution containing 50%solids. The remaining ingredients were stirred into the acetone solutionwhich was then blended with the chopped glass fiber in a mixer. Thismixture was then air dried to remove most of the acetone, then the driedmixture was compounded on a two-roll mill for -2 minutes. The two-rollmill was a differential mill with the fast roll heated to 160 and theslow roll heated to 200 F. The milled product was cooled, granulated andscreened to remove fines. Test specimen were molded from the granulatedmolding compound at 3000 p.s.i. for 5 minutes at C.

Samples molded from the formulations set forth below were tested forthermal stability in a stainless steel pipe bomb, a test chamber madefrom two-inch, inside diameter, stainless steel pipe threaded at eachend to receive an appropriate pipe cap containing a Tefion gasket, asfollows: a piece of silicon rubber (Durometer -A of 60 per ASTM test D-2240-68) was placed between two /2" x A" x 5" bars molded from theformulations set forth below and the test specimens were wired into anassembly with several turns of No. 16 gauge copper wire. The wiredassembly was sealed in the pipe bomb and stored for 72 hours at 220 C.The samples and inside of 4. The composition of claim 1 in which thediallylic phthalate prepolymer is selected from the group consisting ofdiallyl orthophthalate and diallyl isophthalate prepolymers.

5. The composition of claim 4 further comprising up to 200 parts byweight of an inert filler selected from the group consisting of inertmineral fillers and inert fibrous fillers per 100 parts of diallylicphthalate prepolymer.

6. The composition of claim 4 further comprising up to 400 parts byweight of fiber glass per 100 parts of diallylic phthalate prepolymer.

Example 1 Formula:

Diallyl phthalate prepolymer (Dapon 35) Diallyl isophthalate prepolymer(Dapon M) tert-Butyl perbenzoate Calcium stearateVinyl-tris(Z-methoxyethybsilane- Glass strands inch) Hexabromobiphenyl(Firemaster BP-6) Alumina trihydrate (Alcoa 331) Antimony oxide Example2 Comparison Diallyl chlorendate monomer Properties:

Heat deflection temp. C.)

Izod impact (ft. lbs.) 1.37 Rockwell hardness (M) s Mold shrinkage(ilL/il'l.) Water extract conductance (megohm-cm 6 days.. 22 12 days 43-13.0. 10 /10 ,a 1s 4.5 4.4 4.4 4.3 45 4 13.0. 10 /10 Wet.-. LS/4.4.-.-11F. 16 /10, as iS DOS/.006- D.F. 10 /10 wet .OODLOOG. D.C. 1O /10 /l/l0 at 200 C 6.3/5.7/5.3/ D F /lO /l0 /l0 at 200 C .l8/.06/.04/ 03-- Volresistivity (ohm-cm R T 3.0)(10 Surface resistivity (ohm) R T 5.0X10 Volresistivity at 200 C. (ohm-cm 9.0X10 H2O absorption (48 hrs. at 500.)... 0.11 Specific gravity 1.81 Arc resistance, seconds 151 Helicalcoil ignition time (seconds)- 99 Helical coil burning time (seconds) 67Insulation resistance, ohm, wet (16 hrs. at 130 (1)...." 8.0X10Stainless steel pipe bomb test 220 C. for 72 hrs. retained 19,600 10,7004,180.

fiexural strength (p.s.i.). Visual examination: Silicone rubber llghtlss f ened Slightly softened Detenorated to small flakes. Copper wire Br g0 corros Bright, n0 corrosion Black, severely corroded. Bomb interior,phthalic anhydride crystals Very S g amount of Very slight amount ofLarge amount of crystals.

crystals. crystals.

What is claimed is: References Cited 1. A filled, flame-retardant,thermosetting diallylic UNITED STATES PATENTS phthalate moldingcomposltlon containing at least 30% 3,331,797 7/1967 Kopetz et a1 byweight diallyllc phthalate prepolymer WhlCh 1n the h t t d t 1 co rosiveases at 3,362,928 1/1968 Dont e et al. 2604l f 5 i s aledgenvironment3,624,024 11/1971 Caldwell 260'40 R f gis ihg h a i allylic phtha latepr epolymer (b) O 5 344J1535 4/1969 Beocham et 260*40 R i 1 2 t 1. to20% by weight hexabromobiphenyl based on prepoly- 3677999 7/197 Dank e a260 D1g 24 mer, (c) 3 to 60% by weight alumina trihydrate based on OTHERREFERENCES p p y and a Polymerization initiator ill Frankenhotf et 211.:Look Whats Happening in Premix cient amount to convert the moldingcomposition to the thermoset state at elevated temperatures.

2. The flame-retardant composition of claim 1 in which thehexabromobiphenyl is present in the amount of 1.5

to 15% by weight based on diallylic phthalate prepolymar.

3. The flame-retardant composition of claim 1 in which the aluminatr-ihydrate is present in the amount of 8 to 55% by weight based ondiallylic phthalate prepolymer.

Molding Compounds, Plastics Technology (August 1969), pp. 436.

\Chemical Abstracts, 57:16900d Aug. 30, 1962.

ALLAN LIEB EEMAN, Primary Examiner S. M. PERSO'N, Assistant ExaminerU.S. Cl. X.R.

260-40 R, Dig. 24, 42.44, 42.52

